Generally, when muscles are not regularly trained, the muscular function will be impaired due to aging, and decreases in muscle mass and neuromuscular junctions (motor unit) will occur, and thus the body will feel fatigue easily and will become languid, thus reducing the vital power of the body and rapidly reducing the quality of life (J. Appl. Physiol. 2003, 95, p 1717-1727). For this reason, it is recommended that exercise such as resistance training be regularly performed (Korean Patent Laid-Open Publication No. 10-2009-0089815) together with suitable dietary therapy. As described above, regular exercise is required to improve the quality of life, and not only athletes but also general people require more energy and endurance in daily life. However, modern people who are pressed with a busy daily life mostly tend to depend on dietary supplements. Thus, studies on supplements, functional foods, food compositions and the like for improving physical exercise performance ability have been conducted for a long period of time. In fact, it is known that the intake of compounds such as steroids and caffeine increases exercise capability. However, such drugs can be accompanied with fatal side effects, and thus the use thereof is extremely limited.
Skeletal muscle fibers are generally classified into type 1 (oxidative/slow) and type 2 (glycolytic/fast) fibers, and there are significant differences in contraction, metabolism and susceptibility to fatigue between muscle fiber types. Type 1 fiber is rich in mitochondria and uses oxidative metabolism to produce energy, and thus can steadily supply ATP for a long period of time to resist fatigue. Accordingly, muscle consumption does not occur in skeletal muscles rich in type 1 fiber (Muscle Nerve 2005, 31, p 339-348). Type 2 fiber lacks mitochondria and oxidative enzymes and depends on glycolytic metabolism as a major energy resource, and thus is easily fatigued.
PPAR-δ (peroxisome proliferator activated receptor δ) is a major transcription regulator which is abundantly present mainly in skeletal muscles, particularly type 1 fiber (10 folds of PPAR-α, and 50 folds of PPAR-γ) and activates enzymes associated with the beta oxidation of long-chain fatty acids to burn fat in adipose cells (Cell 2003, 113, p 159-170). Also, it is a first transcription factor that stimulates the formation of type 1 fiber. It is known that PPAR-δ regulates mitochondrial biosynthesis when being activated and is involved in complex pathways which improve exercise capability and increase resistance to obesity (PLOS Biology 2004, 2, p 1532-1539). Thus, type 1 fiber made adaptively by exercise is known to have high resistance to fatigue. Thus, it was reported that the artificial overexpression of PPAR-δ shows the same effects as exercise. When PPAR-δ was artificially overexpressed in the muscles of mice, mitochondrial biosynthesis increased and the expression of fatty acid beta-oxidase and type 1 muscle fiber also increased, and thus continuous running time and distance increased by 67% and 92%, respectively, compared to those for general mice (PLOS Biology 2004, 2, p 1532-1539). Therefore, when PPAR-δ is activated, the type of muscle fiber can be changed, resulting in an increase in exercise performance ability.